Modulation of lipopolysaccharide-induced neuronal response by activation of the enteric nervous system.
Résumé
Background:
Evidence continues to mount concerning the importance of the enteric nervous system (ENS) in
controlling numerous intestinal functions in addition to motility and epithelial functions. Nevertheless, little is
known concerning the direct participation of the ENS in the inflammatory response of the gut during infectious or
inflammatory insults. In the present study we analyzed the ENS response to bacterial lipopolysaccharide, in
particular the production of a major proinflammatory cytokine, tumor necrosis factor-alpha (TNF-
α
).
Methods:
TNF-
α
expression (measured by qPCR, quantitative Polymerase Chain Reaction) and production
(measured by ELISA) were measured in human longitudinal muscle-myenteric plexus (LMMP) and rat ENS primary
cultures (rENSpc). They were either treated or not treated with lipopolysaccharide (LPS) in the presence or not of
electrical field stimulation (EFS). Activation of extracellular signal-regulated kinase (ERK) and 5
?
-adenosine
monophosphate-activated protein kinase (AMPK) pathways was analyzed by immunocytochemistry and Western
blot analysis. Their implications were studied using specific inhibitors (U0126, mitogen-activated protein kinase
kinase, MEK, inhibitor and C compound, AMPK inhibitor). We also analyzed toll-like receptor 2 (TLR2) expression and
interleukin-6 (IL-6) production after LPS treatment simultaneously with EFS or TNF-
α
-neutralizing antibody.
Results:
Treatment of human LMMP or rENSpc with LPS induced an increase in TNF-
α
production. Activation of the
ENS by EFS significantly inhibited TNF-
α
production. This regulation occurred at the transcriptional level. Signaling
analyses showed that LPS induced activation of ERK but not AMPK, which was constitutively activated in rENSpc
neurons. Both U0126 and C compound almost completely prevented LPS-induced TNF-
α
production. In the presence
of LPS, EFS inhibited the ERK and AMPK pathways. In addition, we demonstrated using TNF-
α
-neutralizing antibody that
LPS-induced TNF-
α
production increased TLR2 expression and reduced IL-6 production.
Conclusions:
Our results show that LPS induced TNF-
α
production by enteric neurons through activation of the
canonical ERK pathway and also in an AMPK-dependent manner. ENS activation through the inhibition of these
pathways decreased TNF-
α
production, thereby modulating the inflammatory response induced by endotoxin.
Domaines
Neurosciences [q-bio.NC]
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